The self-proclaimed "true universal open source database," Firebird has been under development since 1981. It boasts "excellent concurrency, high performance, and powerful language support for stored procedures and triggers." Operating System: Windows (7, Vista, XP, NT, ME, 9x, Server 2000, Server 2003, Server 2008), Linux, Unix, OS X, Solaris
PostgreSQL calls itself "the world's most advanced open source database." Key features include support for multiple platforms, full ACID compliance, support for multiple programming languages, Multi-Version Concurrency Control (MVCC), point in time recovery, tablespaces, asynchronous replication, nested transactions (savepoints), online/hot backups and more. Operating System: Windows, Linux, OS X
If your system is running slow or you have concerns about privacy, BleachBit is for you. It can securely delete files and clean out your Internet history, cache, temporary files, logs, cookies and other junk. Operating System: Windows (7, Vista, XP), Linux
DBAN securely deletes all of the information on a hard drive. It's a great tool to have on hand when you're recycling old systems. Operating System: OS Independent
32. Electric Sheep
One of the most interesting screensavers ever created, Electric Sheep connects thousands of "sleeping" systems to create collaborative pieces of art. The name and the concept come from Philip K. Dick's novel Do Androids Dream of Electric Sheep? Operating System: Windows (XP or newer), Linux, OS X, Android, iOS
Leave yourself digital sticky notes on your desktop. Key PNotes features include portability, rich text formatting options, skins, overdue tracking, LAN exchange, social network integration, password protection, encryption, tags and much more. Operating System: Windows (8, 7, Vista)
One of the great features of desktop Linux is the ability to create virtual desktops; VirtuaWin adds the same functionality to Windows. Excellent for multi-tasking, it allows you to group together sets of open windows and switch between them. Operating System: Windows (7, Vista, 2003, XP, 2000, NT, ME, 9x)
Suitable for professional use, Scribus is an advanced page layout program similar to Publisher, QuarkXpress or InDesign. It can create press-ready output or PDFs. Operating System: Windows (8, 7, Vista, 2000, Server 200x, Linux, OS X
If you already use the Firefox browser, Thunderbird makes a great companion app as it offers an email client with a similar interface. To make it more like Outlook, you can also add Lightning for calendar functionality. Operating System: Windows (7, Vista, XP, 2000, Server 2003), Linux, OS X
This very popular Windows encryption app boasts nearly 3 million registered users. It integrates with Windows Explorer—just right-click to encrypt files and double-click to open them. It also works with cloud storage services like DropBox and Google Drive. Operating System: Windows (8, 7, Vista, XP, 2003)
Encrypt your files or mail using GNU Privacy Guard (GPG) technology. It's easy to install and use, and professional support is available from third-party companies. Operating System: Windows (8, 7, Vista, XP)
Another very popular encryption option, TrueCrypt can encrypt an entire disk or a partition. It offers fast performance thanks to parallelization and pipelining features. Operating System: Windows (7, Vista, XP), Linux, OS X.
This community-managed ERP solution includes HR, sales, purchasing, manufacturing, materials, finance, maintenance and project management features. It integrates with several other well-known open source enterprise applications to add ecommerce, business intelligence, document management and other capabilities. Operating System: Windows, Linux, OS X, others
41. Apache OFBiz
Managed by the Apache Foundation, this enterprise automation suite includes CRM, e-commerce, supply chain, manufacturing, maintenance management, and point of sale capabilities, as well as traditional ERP features. It attempts to be "as good or better than those available from major proprietary ERPs at a significantly lower total project cost." Operating System: OS Independent
This award-winning software boasts that it's the "most modern, adaptable and lowest cost ERP solution available." It's available in enterprise or community editions, as well as a cloud-ready version. Operating System: Windows, Linux, OS X
The "leading Web-based business applications for the cloud," Openbravo is a suite of Web-based software for managing businesses. In addition to the free community version, it comes in several paid versions, including some tailored for various vertical markets. Operating System: OS Independent
The self-proclaimed "worlds #1 open source ERP software" comes in multiple cloud-based or on-site versions, in addition to the free PostBooks edition. Paid add-ons, services and support are also offered. Operating System: Windows, Linux, Unix, OS X
45. 0 A.D.
This award-winning real-time strategy game is similar to Age of Empires. Players choose a civilization and build their cities while combating opponents. Operating System: Linux, Windows (8, 7, Vista, XP, 2000), OS X
46. Alien Arena
A fast-paced first-person shooter, Alien Arena offers "immersive arenas, freaky and violent weapons, and a vibrant community." That graphics are excellent, and there are plenty of online games to connect with. Operating System: Linux, Windows, OS X.
Another first-person shooter, AssaultCube Reloaded aims to incorporate some of the best features from various commercial games. Key features include ricochet shots, anti-cheat, many different wapons, realistic gameplay and more. Operating System: Windows (7, Vista, 2000, Server 2003), Linux
This incredibly sophisticated flight simulator rivals commercial applications. It includes realistic models of more than 20,000 real airports and many different aircraft. Plus, the active community of users is always expanding its capabilities with new planes and additional scenery. Operating System: Windows (8, 7, Vista, XP), Linux, OS X, others
49. Frets on Fire
Very similar to Guitar Hero, Frets on Fire challenges users to play along with their favorite songs using a guitar controller or the keyboard. You can create your own songs, import songs created by the community of users or import Guitar Hero songs. Operating System: Windows, Linux, OS X
Designed for young children, this project brings together more than a hundred different educational games. It includes activities related to math, keyboarding, piano composition, geography, science, chess, reading and much more. Operating System: Windows (7, Vista, XP, 2000), Linux.
In this real-time strategy game, players choose to play as Tech, Magic, Egypt, Indians, Norsemen, Persian or Romans. The game world is incredibly detailed and many multi-player game servers are available. Operating System: Windows, Linux
This excellent Texas Hold 'Em app offers both single- and multi-player games. The interface is very attractive and you can easily change the style or create one of your own. Operating System: Windows, Linux, OS X, Android